166 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Hydrogen-metal Flutings. 



With the exception of tin, every metal thus far examined in the 

 rotating metallic arc in hydrogen gives a characteristic set of spectrum 

 lines which are not found in the arc in air. Inasmuch as compounds of 

 hydrogen with some metals are known, I have, in lieu of a better hypoth- 

 esis, supposed that these lines are due to such compounds formed in the 

 arc. No new isolated lines, surely due to hydrogen, have been found. 

 The following description takes up the metals in the order of the relative 

 intensities of these flutings. 



Tin. 



No fluting has been discovered due to a combination of tin and hydro- 

 gen. There are four lines of intensity ^ on Rowland's scale, at ap- 

 proximately 3715, 3841, 4245, and 4386, which have not yet been 

 identified. These may be weak tin lines not listed, or weak impurity 

 lines. The deposit which is formed in the hood enclosing the arc is very 

 small in amount and of a greenish color, and consists of very small 

 globules. If this deposit is heated upon platinum foil in a Bunsen flame 

 it quickly glows, and thereafter has a slate color ; and if this powder is 

 placed in hydrochloric acid it dissolves when heat is applied and gives 

 off bubbles of gas. If the dark powder, after the first heating, is reheated 

 on foil in the flame, it glows again, apparently at a higher temperature 

 than before, and then becomes a very white powder, both of which ex- 

 periments go to show that the original powder is not metallic tin but is 

 possibly some combination of tin and hydrogen. 



Coin Silver. 



This metal gives a delicate fluting with first head at 3333.86 and run- 

 ning toward longer wave lengths. There are only about fifty lines in 

 this fluting, and they have an average intensity rather less than ^ on 

 Rowland's scale. 



Copper. 



This metal gives a rather open fluting, having the head at 4279,77 and 

 running toward the longer wave lengths. The number of lines in this 

 fluting is about sixty, and they are individually stronger than those of the 

 coin-silver fluting. This fluting makes its appearance also when an 

 atmosphere of ammonia or of steam is used. The deposit formed inside 

 the hood is rather small in amount and of a brown color. The following 

 table gives the wave lengths of the hydrogen-copper flutings : — 



